ARM: imx: Convert DH i.MX6 DHSOM to DM_SERIAL

Enable CONFIG_DM_SERIAL on DH i.MX6 DHSOM to convert it to DM serial .

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/dh_imx6_defconfig b/configs/dh_imx6_defconfig
index 12e73d9..3487cc2 100644
--- a/configs/dh_imx6_defconfig
+++ b/configs/dh_imx6_defconfig
@@ -98,6 +98,7 @@
 CONFIG_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_SCSI=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y